In this Aug. 1, 2016, photo, Robert DeLeo, the speaker of the Massachusetts House of Representatives, speaks at a bill signing ceremony at the Statehouse in Boston. Credit: Elise Amendola / AP

BOSTON — Robert DeLeo, the speaker of the Massachusetts House of Representatives, announced his resignation on Monday in a letter read to members in the chamber.

The Winthrop Democrat’s resignation is effective at 6 p.m. Tuesday.

“It has been an honor and a privilege serving as a member of this institution for almost 30 years,” DeLeo, the longest-serving speaker in state history, said in his letter. “The faith and trust my colleagues placed in me by electing me as their speaker for a record six consecutive terms fills me with a profound sense of gratitude and appreciation. My pride with what we have collectively accomplished over the last 12 years will never be diminished.”

DeLeo is expected to accept a job at Northeastern University, his alma mater.

Northeastern on Monday did not disclose what DeLeo would do at the university, but in a statement said, “Pending ongoing conversations, we are looking forward to welcoming Speaker DeLeo back to his alma mater.”

First elected in 1991, DeLeo has been speaker for 12 years, taking over after the January 2009 resignation of former Democratic Speaker Salvatore DiMasi, who was later convicted of federal corruption charges including conspiracy, extortion and theft of honest services by fraud. He ended up serving five years of an eight-year prison sentence.

The two Democratic speakers preceding DiMasi — Thomas Finneran and Charles Flaherty — also left under a cloud, both pleading guilty to federal charges, although neither served prison time.

Ron Mariano, a Quincy Democrat, the current majority leader, is considered a likely successor to DeLeo. Mariano declared his candidacy earlier this month when DeLeo’s possible resignation came to light in an ethics disclosure.

“I believe I have earned the trust and confidence of my colleagues and that I have gained their support to lead the House forward,” he said in a statement.

The speaker wields enormous power. The speaker can reward supporters with plum committee assignments and extra stipends while also punishing critics and blocking bills he opposes while pushing others that he favors.

A Democratic caucus to elect a new speaker has been scheduled for Wednesday.